Method of concentrating fluorspar ores



Patented Feb. 21, 1950 2,497,863 METHOD OF CONClgNTIgA'ElNG FLUORSPAB Julius Bruce Clemmer, Tucson, Ariz., and Ballard H. Clemmons, Tuscaloosa, Ala., assignors to the United States of America as represented by the Secretary of the interior No Drawing. Application March 21, 1946, Serial No. 656,122

Claims. (Cl. 209l.6\6)

(Granted under the act of March 3, 1883, an amended April 30, 1928; 370 0. G. 757) The invention described herein may be manufactured and used by or for the Government of the United States for governmental purposes without the payment to us of any royalty thereon in accordance with the provisions of the act of April 30, 1928 (ch. 460, 45 Stat. L. 467).

This invention relates to an improved process for the concentration of fluorspar ores by froth flotation; more particularly it relates to the froth flotation of fluorspar from pulps containing calcite or barite.

In our co-pending application, now Patent No. 2,407,651, filed November 1, 1944, we have described a method for froth flotation of fluorspar from ores containing calcite, barite, quartz, feldspar and other silicate minerals including clay, and oxidized or sulfide minerals, such as iron oxides, pyrite, galena, and sphalerite, as gangue constituents. The prior method consisted of treating an aqueous pulp of the ground ore with a fluorspar collecting agent selected from the class consisting of fatty acids and soaps in the presence of a soluble inorganic fluoride and a lignin sulphonate, and subjecting the pulp to froth flotation to recover the fluorspar. The examples recorded in that prior application reveal that the combination of a. lignin sulphonate and a soluble inorganic fluoride, such as sodium fluoride or sodium fluosilicate, was particularly efficacious for the retardation of gangue constituents during flotation of the fluorspar values with fatty acid and soap collecting agents.

The present invention is the result of our further discovery that highly satisfactory results may be obtained in practicing the said method with gelatinized starch and dextrinized starch products, such as the British gums and dextrins. We have found that variousstarches and intermediate hydrolyzed products thereof may be used in conjunction with cooperating agents such as sodium fluoride and other soluble inorganic fluorides to effect retardation of quartz, calcite, barite, iron oxides, clay, and other gangue minerals commonly found in fluorspar ores. The lignin sulphonates may be used as auxiliary reagents in conjunction with the starches, gums and dextrins, if desired, but they are not obligatory in the practice of this invention.

Suitable starches are found widely distributed in nature in the tissues of higher plants and make up the larger part of the solids in seeds, bulbs, and tubers. When pure, starch is a white, odorless, tasteless, granular or powdery complex carbohydrate which has been assigned the empirical 3 formula (Cal-11009:. Under the microscope, starch appears as minute. translucent grains of various size and shape depending on its botanical origin. Although the structure of starch granules is still a subject of controversy, starch chemists, in general, believe that the granules are composed of two closely associated starch forms, one of which is soluble in water at room temperature whereas the other is relatively insoluble. The water-insoluble portion, generally designated as amylopectin by starch chemists, is believed to occur as the outer skin of the starch grain, and

envelopes the water-soluble portion, commonly designated as amylose. Natural starch granules are insoluble in water because of the amylopectin envelope. If the envelope is ruptured, however, the enclosed amylose dissolves to yield a gel' or solution depending on the concentration and gelling properties of the particular starch.

Various methods may be used to rupture the amylopectin envelope and facilitate solution of amylose. Mild heat treatment or roasting of the dry starch, or roasting of the starch after treatment with an acid or oxidizing agent, ruptures the granules and thereby increases their water solubility. Starches treated by such methods are variously designated as soluble, roasted, oxidized or pre-gelatinized starches which are common and well known products of commerce. Mechanical rupture of the granules by severe grinding yields a soluble starch product. The formation of starch solutions by boiling is a common and well known method of preparation. When a mixture of starch and water is heated to a certain temperature, the granules expand and rupture to form a gel or solution. The rupturing temperature varies for different starches depending upon botanical origin and past history. Various chemical agents reduce the rupturing temperature and facilitate rapid preparation of starch solutions at room or only slightly elevated temperatures. Caustic alkalies, such as sodium or potassium hydroxide, are particularly effective solubilizing agents for both natural and treated starches. Various metal salts, such as zinc chloride, ferric chloride, or sodium thiocyanate, and certain n0ne1ectr01ytes, such as urea or chloral, exert a marked swelling influence on starch granules and facilitate their solution. These and other methods may be advantageously employed to solubilize starch and yield solutions or gels suitable for the practice of our invention. To avoid confusion in describing our invention, we shall employ the term gelatinized starch to include not only the dry starch products of commerce treated by various methods to enhance their water solubility, but also aqueous gels and solutions of starch prepared by the above described methods.

Starch solutions on prolonged standing at elevated temperature tend to hydrolyze to yield simpier carbohydrates. This hydrolysis is catalyzed by acids and yields glucose when carried to com-.

pletion. Incomplete hydrolysis yields a variety of intermediate products which are commonly designated as dextrins. The dextrins are often named according to the color reaction with iodine; amylo-dextrin, for example, gives a blue color with iodine; erythro-dextrin gives a red color; whereas, achroodextrin gives no change in color with iodine. Progressive hydrolysis of starch yields first the dextrins, amylo-, erythro-, and achroo-, in the order named, then maltose, and finally glucose. Dry starch, or starch moistened with acid, when heated to a temperature of about 200 C. undergoes degradation to yield the so-called British gums and dextrins of commerce. In making British gum, acid is generally omitted and the starch is heated to a higher temperature for a longer period of time. Although the exact chemical structure of the gums and dextrins formed by thermal degradation is a subject of controversy, it is generally believed that they contain products similar to, but not necessarily identical with, those formed from acid hydrolysis of aqueous starch solutions. In describing our invention, we shall use the term "dextrinized starch to include not only the British gums and dextrins of commerce prepared by thermal degradation, but also the intermediate products from hydrolysis of aqueous starch solutions hydrolyzed to an extent not greater than achroodextrin. The sugars, such as maltose or glucose, formed by complete hydrolysis of starch are of little benefit in our method of flotation. In the practice of our invention, we therefore prefer to use dextrinized starches hydrolyzed to an extent not greater than achroo-dextrin and preferably not greater than erythro-dextrin as exhibited by commercial dextrin and British gum.

As a result of long experimentation and research on a variety of fluorspar ores containing quartz, feldspar, calcite, barite, and various other nonsulflde or sulfide gangue minerals, we have discovered that the gelatinized and dextrinized starch products may be employed in conjunction with the soluble inorganic fluorides, or other auxiliary cooperating agents later described, to retard the gangue constituents while floating the fluorspar values with higher fatty acids and soap collectors. The commercial dextrins and British gums are particularly eflicacious for retarding common gangue constituents in fluorspar ores by our method of flotation. The soluble and pregelatinized cereal and tuber starches of commerce are likewise effective gangue depressants but they are somewhat more expensive than the natural starches. The natural starches which we have found satisfactory include various commercial forms of potato, rice, corn, wheat, arrow root, and tapioca starch. Wheat flour and corn meal may also be employed as the starch material and are particularly attractive due to their low cost.

The natural starches were gelatinized by the procedures previously described to yield solutions or gels for flotation use. A convenient procedure employed for preparation of starch solutions was to rupture the granules with caustic soda at room temperature (about 30 C.) to yield a solution containing 1.0 percent starch and 0.25 percent caustic soda; these proportions gave a solution of the desired fluidity for ease of addition to the flotation pulp, but other proportions may be used if desired. The starch solution was prepared by slowly adding with constant stirring a desired quantity of a concentrated caustic soda solution to an aqueous suspension of the starch. The starch granules rapidly swell and rupture on addition of caustic soda to form a gel or solution which may then be diluted to a desired concentration for flotation use. Ease of addition to the pulp favored use of starch solutions of low viscosity containing from 1 to 5 percent starch, but more viscous solutions and gels containing as much as 20 percent starch were found satisfactory.

The quantity of caustic soda required to gelatinize starch decreases with increasing temperature and caustic soda may be omitted if the starch suspension is heated to the rupturing temperature of the particular starch. Solutions of starch gelatinized by boiling were found satisfactory in our method of flotation. Starch solutions prepared by boiling and caustic treatment will hereinafter be designated as boiled starch and causticized starch," respectively.

So far as we are aware the gelatinized or dextrinized starches singly or together with auxiliary cooperating agents, such as sodium fluoride, have not heretofore been employed for the retardation of gangue constituents in the flotation of fluorspar ores. The mechanism of the retarding action of the gelatinized and dextrinized starches on gangue minerals in our method of fluorspar flotation has not been definitely determined and this invention is not limited to any theory of action. It seems probable, however, that an important function of the starch or dextrin is to coat the surfaces of the gangue particles so that they present water-avid surfaces which prevent their attachment to the bubbles in froth flotation. Coating of the gangue particles may be induced as a result of either chemical reaction or adsorption to satiate the surfaces, and this coating prevents or greatly inhibits formation of collector coatings which normally would have formed to render the particles floatable. It may be further assumed that fluorspar particles in the pulp exhibit less tendency than the gangue particles to become coated by the gelatinized or dextrinized starch products, and, as a consequence, the un-satiated fluorspar surfaces may become coated with the collector and thus rendered floatable. Judicious use of gelatinized and dextrinized starch thus enables retardation of the gangue in fluorspar flotation.

The beneficial effect of cooperating agents such as a soluble inorganic fluoride in the flotation of fluorspar when using the gelatinized and dextrinized starches as gangue depressants was readily apparent in the testing of a variety of ores containing barite or calcareous gangue materials. Use of a soluble inorganic fluoride such as sodium fluoride, for example, enabled more rapid and complete flotation of the fluorspar and more effective retardation of the gangue constituents. The mechanism by which the fluorides accomplish these beneficial effects is not definitely known. It seems likely however that one of the important functions of the fluorides is to complex or precipitate soluble salts in the pulp which would otherwise impair selectivity of the separation. The fluorides are effective slime dispersants and may thus aid flotation by assisting in proper dispersion of the pulp. The combined effect of complexing soluble salts and dispersion of the slime may possibly serve to clean the surfaces of. the fiuorspar particles to make them more readily floatable by the higher fatty acid and soap collecting agents. Similar cleaning of the gangue particles renders them more susceptible to retardation by the gelatinized and dextrinized starches. These factors may be effective in varying degree on different ores depending upon the type and quantity of soluble salts present in the pulp and the surface purity of the fiuorspar and gangue minerals.

Our experiments have demonstrated that the fluorides are particularly advantageous and their beneficial eifect is more marked when treating ores containing soluble salts or large amounts of calcite or barite. The need for the fluorides is less apparent and they may be omitted if desired in the flotation of fiuorspar from siliceous ores relatively free of soluble salts or slime gangue constituents. We prefer, however, to use addition agents such as sodium fluoride in the flotation of all fiuorspar ores. Less collector is required and flotation of the fiuorspar is more rapid and complete.

While .a number of cooperating agents may be employed in the practice of our invention, we prefer to use a soluble inorganic fluoride, such as sodium fluoride. Ammonium and potassium fluorides were found equally as effective as sodium fluoride, but they are more expensive. Aluminum fluoride and sodium silicofluoride also proved satisfactory but they exhibited no particular advantages over sodium fluoride and were somewhat less soluble. Hydrofluoric and hydrofiuosilicic acids may also be used in our flotation method if desired. Our experiments on a variety of ores indicate that the soluble inorganic fluorine-bearing compounds which ionize in aqueous solutions to yield the fluoride ion may be used as cooperating agents in our method of flotation.

In the practice of our method of flotation, we have found that a number of auxiliary addition agents may be used in conjunction with the soluble inorganic fluorides and elatinized or dextrinized starches, if desired. Auxiliary addition agents which we have employed and found beneficial include sodium sulfide, sodium sulfite, sodium hydrosulfite, sodium cyanide, potassium dichromate and acidified dichromates, sodium citrate, sodium metaphosphate, trisodium ortho'phosphate, tetrasodium pyrophosphate, soda ash, caustic soda, and sodium silicate, These addition agents apparently serve a' multifold purpose and assist in flotation of the fiuorspar and retardation of the gangue materials by complexing or precipitating soluble salts in the pulp, by establishing the optimum 'pH for flotation, or by aiding dispersion of the slime constituents in the flotation pulp. Fluoride requirements in flotation are generally less when using the auxiliary addition agents. The proper proportions of the various addition agents and the soluble inorganic fluorides vary for different ores and are best determined by trial for any particular case.

We have achieved good flotation of fiuorspar from slightly acid, neutral and moderately alka-= line pulps by the practice of our invention. While precise control of the pH of the pulp is not highly essential for an effective separation, we prefer that the pH be maintained in the range 7 to 10 and we preferably employ a pH of 8.0 to 9.5. The frothing proclivities of the fatty acid and soap collecting agents increase progressively with increase in pH of the pulp and strongly alkaline pains of pH 11 or more should be avoided as the voluminous froths formed are difflcult to control. A pulp pH in the range 7 to 10, however, gave compact, heavily mineralized froths. We have found in many cases that the sodium fluoride employed as a cooperating agent in conjunction with the gelatinized or dextrinized starches gave a pulp of suitable pH for flotation and obviated use of pH modifying agents. A pul of too high pH may be corrected by judicious addition of an inorganic acid and, conversely, a pulp of too low pH may be corrected by addition of a proper quantity of an alkaline reagent such as soda ash, caustic soda, or sodium silicate. The pH modifying agent may be added to the pulp simultaneously with or subsequent to the soluble inorganic fluoride.

Various of the higher fatty acid and soap collecting agents have been found suitable for the flotation of fiuorspar in the practice of this invention. Suitable collectors which we have employed include oleic acid, red oil, crude and purified sodium oleate, fish oil soap, fish liver oil fatty acids, and other higher fatty acids of animal or vegetable origin.

Those skilled in the art of soap flotation concur that good separations are seldom achieved from pulps containing flocculated slime. While we have obtained flotation of fiuorspar from flocculated pulps, we prefer that the pulp be substantially or completely dispersed. The gelatinized starches which we employ as gangue depressants are powerful flocculating agents for both fluorspar and gangue slime under certain conditions, but under other conditions serve as slime dispersants. A small quantity of gelatinized starch added to a fiuorspar pulp may result in complete flocculation of the pulp, whereas further addition of starch may partially or completely redisperse the pulp. The quantity of starch needed to retard calcite or barite during flotation of the fiuorspar is suflicient on many ores to give a dispersed pulp. Other fiuorspar pulps containing abnormal quantities of slime may require an excessive amount of starch to disperse the pulp. On such ores, We may advantageously employ supplementary reagents to disperse the pulp and minimize starch requirements. The dextrinized starches, such as British gum or dextrin, are eifective slime dispersants and may be employed in conjunction with the gelatinized starches. Other organic reagents including various tannin extracts, such as quebracho, oak, hemlock, chestnut, or Borneo cutch, and the lignin sulphonates are particularly effective slime dispersants and may be used in conjunction with the gelatinized or dextrinized starches in the practice of our invention if desired. The lignin sulphonates and tannin extracts in addition to serving as auxiliary slime dispersants also exhibit marked gangue depressing properties which complement those of the gelatinized or dextrinized starches.

In carrying out the flotation process according to this invention, the fiuorspar ore or product to be treated is first ground to proper size for flotation, if not already of such size, by conventional grinding methods. The fineness of the grind may vary from 20 to 200 mesh or finer depending on the locking characteristics of the particular material; substantially complete liberation of the fiuorspar from the gangue is essential for a satisfactory separation, and the fineness of grind should be selected accordingly. The ground material in the form of an aqueous pulp is then subjected to froth flotation to recover the fiuorspar and reject the gangue materials in the following manner: The pulpecl material is conditioned with the desired quantities of a soluble inorganic fluoride. such as sodium or ammonium fluoride; a gelatinized or dextrinized starch; and a fatty acid or soap collecting agent, such as oleic acid or sodium oleate. Also if desired, a pH modifying agent or slime dispersing agent may be employed. The conditioned pulp is ventional mechanical or pneumatic methods to yield an enriched fluorspar froth and a tailing product substantially free of fluorspar and enriched in gangue constituents. The froth product may contain some quartz, calcite, barite, or other gangue materials collected with the fluorspar in the initial frothing operation. The froth is repulped with additional water and refloated to recover a still further enriched fluorspar product by rejecting the remaining gangue. One or more such cleaning steps suffices to yield the final fluorspar concentrate of the desired commercial grade. Additional reagents, such as a small quantity of a gelatinized or dextrinized starch, a soluble fluoride, or a pH modifying agent, may be used in the cleaning steps to facilitate rejection of the gangue constitutents. pine oil, cresylic acid, or an alcohol, may also be used, if desired, to promote flotation of the fluorspar. The tailings material resulting from the cleaning steps, commonly designated as middlings, may be rejected or returned to the preceding flotation step or other convenient points in the flotation or grinding circuit for retreatment.

The practice of our invention is not limited to any particular order of addition of the separate reagents. We prefer, however, to condition the pulp with the fluoride and starch, or other addition agents, before adding the fluorspar collecting agent. The fluorides and other addition agents, singly or together, may be added to the grinding step if desired. Our tests indicate that moderate conditioning of the pulp with the cooperating agents and starch depressants insures adequate retardation of the gangue constituents.

. Likewise, moderate conditioning with the collect- "-ing agent suflices for good flotation of the fluorspar.

The proportions of the several reagents used in practicing our method of flotation are subject to considerable variation for different ores and the proper quantities are best determined by experimentation for any particular case. We have found the invention applicable to a wide variety of fluorspar ores containing barite and siliceous or calcareous gangue materials. Extensive flotation experiments on flurospar ores from domestic and foreign deposits have demonstrated that the invention is particularly advantageous in that it enables recovery of high-grade concentrates from ores which heretofore have been difficult or impossible to separate by known flotation methods. A proper balance of the-gelatinized or dextrinized -starch and the soluble inorganic fluoride effectively retards the gangue and enables rapid and substantially complete flotation of the fluorspar values with a moderate quantity of collector. Moderate variation in the quantities of the starch and fluoride is permissible in the practice of our invention. The wide latitude in reagent control and the effective retardation of gangue constituents accomplished by our procedure as com- .pared to other processes should thereby effect greater operating economies and facilitate recovery of fluorspar from ores heretofore dificult to treat.

then froth floated by con- A frothing agent, such as The invention will be further illustrated but is not intended to be limited by the following examples of practice. The quantities of the separate reagents employed in the recorded tests are expressed in conventional terms of pounds of reagents per ton of flotation feed.

Example I A sample of fluorspar ore from a New Hampshire deposit was obtained for flotation testing. The ore consisted essentially of fluorspar associated with quartz, feldspar and barite. A head analysis of the ore gave 28.4 percent CaFz, 0.2 percent CaCOs, 64.7 percent SiOz, and 6.0 percent B21504.

The ore was stage crushed in rolls to pass 20 mesh and used as the feed for subsequent flotation procedures. A 250-gram portion of the'ore was wet ground to pass 65 mesh in a conventional laboratory pebble mill. The ground charge was allowed to settle and the clear, supernatant water was carefully decanted from the solids to avoid loss of slime. The solids were repulped with tap water and transferred to a small mechanical flotation cell of standard design. Additional tap water was added to the cell to give a pulp containing about 25 percent solids for flotation. The pulp was conditioned 2.5 minutes with the equivalent of 2.0 pounds per ton of commercial sodium fluoride of insecticide grade. The equivalent of 2.0 pounds per ton of commercial corn dextrin No. 152, marketed by the Corn Products Refining Company, New York, N. Y., was then added and the pulp again conditioned for 2.5 minutes. Finally, the ulp was conditioned with the equivalent of 0.32 pound per ton of Darling red oil, a commercial oleic acid marketed by Darling and Company, Chicago, 111. Air was then allowed to enter the cell and resulted in immediate formation of a compact, heavily mineralized fluorspar froth. The froth was collected for 4 minutes whereupon the roughing operation was completed. The rougher froth was triple cleaned by refloating in the same cell using tap water for dilution and 0.50 pound per ton of corn dextrin No. 152 in each step to retard the remaining gangue and yield the final fluorspar concentrate. The flotation products were subsequently dried, weighed, and analyzed.

The fluorspar concentrate represented a weight recovery of 27.7 percent, assayed 97.7 percent CaFz, 0.2 percent CaCOa, 0.4 percent SiOz, and 1.7 percent BaSO4, and accounted for a recovery of 94.9 percent of the fluorspar in the feed. The roughing and cleaning steps rejected 92 percent ;)f the barite and 99.6 percent of the silica in the eed.

. The results of the recorded test are typical of those obtained using various soluble inorganic fluorides as the cooperating agent in conjunction with commercial dextrins and dextrinized starches prepared in the laboratory 'by acid hydrolysis.

Example 11 Another 250-gram portion of the New Hampshire fluorspar ore was prepared and floated by the procedure described in Example I. Globe gum 160, a commercial British gum marketed by the Corn Products Refining Company, New York, N. Y., was employed as the gangue depressant in conjunction with insecticide-grade sodium fluoride and red oil. The quantities of the reagents employed were in the roughing step 4.0, 2.0, and 0.24 pound per ton, respectively. The rougher froth was triple cleaned by refioating in the same cell using tap water for dilution and without additional reagents.

The final cleaner concentrate represented a recovery of 90.6 percent of the fluorspar in the feed and assayed 99.3 percent CaFz, 0.2 percent CaCOa, 0.2 percent Si02, and 0.3 percent BaSO4.

A duplicate of the preceding test in which a dextrinized starch lproduct designated as Reagent 633," marketed by American Cyanamid Company, New York, N. Y., was employed as the gangue depressant gave a fluorspar concentrate which assayed 99.1 percent CaFz, 0.2 percent CaCOs, 0.4 percent SiOz, and 0.3 percent BaSO4. The concentrate represented a recovery of 95.7 percent of the fluorspar. Roughing and cleaning rejected 98.8 percent of the barite and 99.8 percent of the silica.

10 Example V The examples of practice described heretofore demonstrate the applicability of this invention for the recovery of fluorspar from ores containing siliceous or calcareous gangue constituents with only minor quantities of barite. We shall now consider the results obtained by its practice on a fluorspar ore containing a substantial amount of barite together with calcite and quartz. The sample was from a Canadian deposit and assayed 52.5 percent CaF'z. 8.6 percent CaCOa, 0.6 percent 5102, and 37.8 percent BaSOr.

A representative portion of the Canadian fluorspar-barite ore was wet ground to pass 65 mesh in a laboratory pebble mill and froth floated employing the following reagents expressed in con-- ventional pounds per ton of feed.

Example III Conditioner Cleaner Reagent Roughor No. 1 No. 2 No. 1 No. 2 No. 3

Sodium fluoride. 1.0 Boiled potato starch 2. 0 0. 5 0. 2 0. 2 Sodium silicate 0.5 Oleic acid 0. 48 pl; of pulp. 9. 4 9.3 9.1 3.3 8. 2 8.2 Time (min.) 5 5 3 2. 5 2. 5 2. 5

The pulp was first conditioned for 5 minutes with the recorded quantities of sodium fluoride, commercial potato starch gelatinized by boiling, and sodium silicate. Oleic acid was then added and the pulp again conditioned for 5 minutes. The rougher froth was triple cleaned using boiled potato starch in each step to retard the remaining gangue and yield the final fluorspar concentrate. The concentrate represented a recovery of 80.5 percent of the fluorspar in the feed and assayed-97.2 percent CaFz, 2.3 percent CaCOa, and 0.1 percent SiOz.

Example IV A duplicate of the preceding test on the Southern Illinois tailing sample using potato starch gelatinized by caustic treatment yielded a concentrate which assayed 97.7 percent CaFa, 2.1 percent CaCOa, and 0.1 percent SiOz, and accounted for a recovery of 79.2 percent of the fluorspar in the feed.

The commercial potato starch was gelatinized by treatment with caustic soda at room temperature (30 C.) to yield a starch solution containing 1.0 percent starch and 0.5 percent caustic. Addition of the causticized starch and sodium fluoride to the flotation pulp gave a pulp having an excessively high pH for flotation. Sulfuric acid was then added to reduce the pH to the preferred operating range. Flotation of fluorspar from the retarded barite, calcite, and quartz was achieved by employing oleic acid as the collector. Roughing and triple cleaning of the froth yielded a final concentrate which assayed 97.5 percent CaFz, 2.0 percent CaCOa, 0.19 percent SiOz, and 0.13 percent E3504, and represented a recovery of 79.5 percent of the fluorspar in the feed.

Ea'ample VI by boiling as the gangue depressant, and sodium I fluoride as the cooperating agent. The quantities of the separate reagents and the flotation periods for the test were as follows:

Conditioner Cleaner Reagent Rougher Sodium fluoride. Boiled potato starch. Oleic acid Frother B-23 Time (min.)

The concentrate represented a recovery of 81.1 percent of the fluorspar in the feed and assayed 98.1 percent CaFz, 0.4 percent CaCOz, 0.1 percent S102, and 0.16 percent B3504.

A duplicate of the above test employing boiled wheat starch as the gangue depressant reagent gave a concentrate which assayed 98.4 percent Car's, 0.4 percent CaCOa, 0.1 percent SiOaand 11 0.23 percent 32.804, and represented a recovery of 68.1 percent of the fluorspar.

A similar test in which corn starch gelatinized by boiling was employed yielded a concentrate which assayed 98.7 percent CaFz, 0.5 percent CaCOzi, 0.1 percent SiO2, and 0.54 percent BaSOr, and accounted for a recovery of 77.8 percent of the fluorspar in the feed.

In yet another duplicate test, soluble starch marketed by the J. T. Baker Chemical Company, Phillipsburg, N. J., was employed as the gangue depressant together with sodium fluoride as the cooperating agent and oleic acid as the collecting agent. The concentrate accounted for a recovery of 74.5 percent of the fluorspar in the feed, and assayed 98.6 percent CaFz, 0.5 percent CaCOa, 0.15 percent SiO2, and 0.09 percent BaSO4.

Example VII The utility of the dextrinized starches was demonstrated by the following test on the Canadian fluorspar-barite ore. A portion of the ore was wet ground to pass 65 mesh in a laboratory pebble mill and froth floated using the The recovered concentrate accounted for 89.5 percent of the fiuorspar in the feed and assayed 95.1 percent CaFz, 2.2 percent CaCOa, 0.3 percent SiOz, and 2.64 percent BaSO4.

Example VIII A duplicate of the test recorded in Example VII in which 0.5 pound per ton of acidified potassium dichromate was employed as the auxiliary addition agent yielded a concentrate which assayed 98.2 percent CaFr, 1.1 percent CaCOa, 0.15 percent S102, and 0.21 percent BaSO4. The concentrate represented a recovery of 72.5 percent of the fluorspar in the feed.

The acidified dichromate solution used in the test was prepared to contain equal proportions by weight of potassium dichromate and sulfuric acid. While the precise function of the aciddichromate in flotation is not known, numerous flotation tests on barite-bearing fluorspar ores have demonstrated that it is a useful auxiliary addition agent in the practice of our invention in that it complements the gelatinized and dextrinized starches and enables more complete retardation of barite.

Example IX In another test on the Canadian sample, aciddichromate was employed as the auxiliary addition agent in conjunction with sodium fluoride, corn dextrin No. 152, and oleic acid. The quantitles of the reagents used in the roughing step were 0.2, 2.0, 4.0, and 0.32 pound per ton of feed, respectively. The rougher froth was triple cleaned using 0.5 pound per ton of dextrin No. 152 in each step to retard the gangue floated in the roughing operation. The recovered concentrate assayed 98.5 percent CaF'z, 1.9 percent CaCOs, 0.2 percent S102, and 0.42 percent BaSOa and accounted for 21.3 percent of the fluorspar in the ore.

Example 2 Dextrinized potato starch prepared by acid hydrolysis was employed as the gangue depressant in another test on the Canadian ore. The dextrin was prepared in the following manner: A two-percent solution of potato starch prepared by boiling was acidified with sulfuric acid to a pH of 3 and reheated to boiling for about 5 minutes to hydrolyze the starch to erythro-dextrln as determined by the conventional iodine-color reaction. The erythro-dextrin solution was rapidly cooled to room temperature and neutralized with caustic soda to inhibit further hydrolysis. The resulting solution was diluted to give a one percent solution, based on the starch originally present, for use in flotation.

This dextrinized starch was used in coniunction with sodium fluoride and oleic acid in treating a second sample of Canadian ore. This material contained 26.8 percent CaFz, 6.0 pergegt CaCOa, 65.7 percent Bea/B04, and 0.6 percent A representative portion of the ore was wet ground to pass mesh in a laboratory pebble mill and froth floated employing the following reagents expressed in pounds per ton of feed.

Potato erythro dex- The concentrate represented a recovery of '74 percent of the fluorspar in the feed and assayed 94.0 percent CaFz, 4.2 percent 08.00:, 1.45 percent BaSO4, 0.08 percent 810:.

Example XI Conditioner Cleaner Rougher Sodium fluoride. Dextrin 152 l Chestnut extract Oieic acid Frother 18-23 it P31531113:

R film eonbmerciai dextrinized starch marketed by Corn Products e ng o.

1 A commercial tannin marketed by Champion Paper and Fiber 00., Canton, N. C

The concentrate assayed 97.6 percent CaF'z. 0.95 percent CaCOa, 0.75 percent B8504, 0.19 percent S102 and represented a recovery of 82.7 percent of the fluorite present in the feed.

Example XII A similar test utilizing Marathon M, a commercial lignin sulfonate marketed by the Mara.-

What is claimed: 1. The process of concentrating fluorspar by f froth flotation of values, I ubl inorganic fluoride, a gelatinized starch, a

. 7tn10,'and

= selected from the class consisting of higher fatty 'acids and their soaps,

thon Chemical Company, Rothschild, Wis., as an addition agent in conjunction with sodium fluoride, Dextrin 152, and oleic acid, demonstrates the utility of this reagent combination.

A portion of the Canadian ore described in Example V was wet groundin a laboratory pebble mill and froth floated using the following reagent charge:

Conditioner Cleaner 10 R D .it Rougher No.1 No.2 No.1 No.2 No.3

Sodium fluoride 2.0 Dextrin 152 2.0 0.5 0.2 15 Marathon M. 1.0 Oleic acid... H of ulp... ime min.)

The concentrates contained 98.4 percent CaFz. 0.45 percent CaCOa, 0.85 percent E2504, 0.19 percent S102 and represented a recovery of 87.4 percent of the fluorite present in the feed.

While we have disclosed the preferred embodiment of our invention, it will be readily apparent to those skilled in the art that many variations and modifications may be made therein without departing from the spirit and scope of the invention as defined in the appended claims.

pulps containing fluorspar comprising adding to such a pulp a so]- pH modifying agent to establish a pH of about at least one fluorspar collecting agent and subjecting said pulp to froth flotation to recover in the froth an enriched fluorspar concentrate.

2. The process of concentrating fluorspar by froth flotation oi pulps containing fluorspar values, comprisin-gadding to such a pulp sodium. fluoride, a gelatinized starch, a pH modifying agent to establish a pH of about 7 to 10, and at least one fluorspar collecting agent selected from the class consisting of higher fatty acids and their soaps, and subjecting said pulp to froth flotation to recover in the froth .an enriched fluorspar concentrate. v

3. The process of concentrating fluorspar by froth flotation of pulps containing fluorspar values, comprising adding to such a pulp a soluble inorganic fluoride, a dextrinized starch, a pH modifying agent to establish a pH of about 7 to 10, and at least one fluorspar collecting agent selected from the class consisting of higher fatty acids and their soaps, and subjecting said pulp to froth flotation to recover in the froth an enriched fluorspar concentrate.

4. The process of concentrating fluorspar by froth flotation of pulps containing fluorspar values, comprising adding to such a pulp sodium fluoride, a dextrinized starch, a pH modifying agent to establish a pH of about 7 to 10, and at least one fluorspar collecting agent selected from the class consisting of higher fatty acids and their soaps, and subjecting said pulp to froth flotation to recover in the froth an enriched fluorspar concentrate.

5. A process of concentrating fluorspar by froth flotation of pulps containing fluorspar values. which comprises subjecting such a pulp to frothflotation treatment at a pulp pH of about pH 7 to pH 10 in the presence of a soluble inorganic fluoride, at least one processed starch product selected from the group consisting of gelatiitized starch, and dextrinized starch, and in the con current presence of at least one collecting agent selected from the group consisting of higher fatty acids and soaps, whereby the fluorspar values are floated and recovered in the froth.

JULIUS BRUCE CLEMMER. .BALLARD H. CLEMMONS.

REFERENCES orrnp The following references file of this patent:

UNITED STATES PATENTS are of record in the Number Name Date 7 2,145,206 Booth Jan. 24, 1939 2,238,662 Shepard Apr. 15 1941 2,327,408 Ellis Aug. 24, 1943 2,363,104 Weinig Nov. 21, 1944 2,364,777 Brown Dec. 12, 1944 2,403,481 Clemmer et al. July 9, 1946 2,407,651 Clemmer et a1. Sept. 17, 1946 2,410,770 Booth et a1. Nov. 5, 1946 

5. A PROCESS OF CONCENTRATING FLUORSPAR BY FROTH FLOTATION OF PULPS CONTAINING FLUORSPAR VALUES, WHICH COMPRISES SUBJECTING SUCH A PULP TO FROTHFLOTATION TREATMENT AT A PULP PH OF ABOUT PH 7 TO PH 10 IN THE PRESENCE OF A SOLUBLE INORGANIC FLUORIDE, AT LEAST ONE PROCESSED STARCH PRODUCT SELECTED FROM THE GROUP CONSISTING OF GELATINIZED STARCH, AND DEXTRINIZED STARCH, AND IN THE CONCURRENT PRESENCE OF AT LEAST ONE COLLECTING AGENT SELECTED FROM THE GROUP CONSISTING OF HIGHER FATTY ACIDS AND SOAPS, WHEREBY THE FLUORSPAR VALUES ARE FLOATED AND RECOVERED IN THE FROTH. 